
SPECIHEN PAGES. 



ELEMENTARY 



PHYSICAL GEOGRAPHY 



BY 



RALPH S. TARR, B.S., F.G.S.A. 

ASSISTANT PROFESSOR OF DYNAMIC GEOLOGY AND PHYSICAL 

GEOGRAPHY AT CORNELL UNIVERSITY 
AUTHOR OF "ECONOMIC GEOLOGY OF THE UNITED STATES" 




Keto gork 
MACMILLAN AND CO. 

AND LONDON 

1895 

All rights reserved 



Macmillan & Co. 

Take pleasure in announcing that the 

Elementary Physical Geography 

By 
Ralph Stockton Tarr, B.S., F.G.S.A., 

j4ssistant Professor of Geology and Physical Geography at Cornell University, 
Author of "Economic Geology of the United States," etc., 

announced some tune since as in preparation, 
will be ready for publication about the first 
of October. 

Teachers are invited to examine carefully 
the following sample pages. The complete 
work will be sent on application without 
charge to any teacher who wishes to examine 
it with the expectation of introducing it as 
a class text-book if found satisfactory. Such 
applications should state the name of the 
school with which the writer is connected 
and the number of copies likely to be ordered 
in case of introduction. 




Plate 1. — Frontispiece. 
Watkins Glen. N.Y. A post-glacial gorge in a shale rock. 



SPECIHEN PAGES. 



ELEMENTARY 



PHYSICAL GEOGRAPHY 



.1^' 



/b 



BY 



RALPH S^^'TARR, B.S., F.G.S.A. 

ASSISTANT PROFESSOR OF DYNAMIC GEOLOGY AND PHYSICAL 

GEOGRAPHY AT CORNELL UNIVERSITY 
AUTHOR OF "economic GEOLOGY OF THE UNITED STATES" 



^ 



^ 



i 




M ACM ILL AN AND CO. 

AND LONDON 

1895 



Ail rights reserved 



COPTKIGHT, 1895, 

By MACMILLAN AND CO. 



Nortoooti iprrss 

J. S. Oushing & Co. — Berwick & Smith 
Norwood Mass. U.S.A. 



PREFACE. 

For some time there have been indications that new text- 
books on ph3'sical geography are demanded ; and in the 
report of the Committee of Ten this finds definite expression. 
In the preparation of this book, wliieh has been in hand for 
several years, there is an attempt to meet this apparent 
demand ; but for reasons which are obvious to many, it has 
not seemed wise to attempt to follow the somewhat radical 
suggestions which were made by the majority of tlie geogra- 
phy conference of the Committee of Ten. Therefore, while 
the physiographic side is given more prominence than is 
customary in works of this kind, this book attempts to only 
partly meet the Committee's suggestions. 

In the preparation of the l)Ook, effort has been made to 
introduce new material, particularly in the illustrations, 
which are a prominent part of the book. Also, there has 
been an endeavor to make the book scientifically accurate, 
and to introduce the latest knowledge on tiles' subjects 
treated. There are probably places in which this is not 
done, for the field is so large that much must be compilation ; 
and the compiler is liable to fall into error. 

I anticipate criticism of the order of presentation, of the 
relative amount of space allotted the various topics, of the 



viii PREFACE. 

omission of some subjects which are usually found in such 
books, and of the inclusion of some not usually discussed : 
but these matters have been carefully considered, and the 
book is the result of a well-matured plan. In many respects 
it is experimental, but it is a deliberate attempt to supply a 
book which is certainly needed. It should not be inferred 
that the author is satisfied with the attempt, — he is keenly 
disappointed at the constant necessity of saving space and 
thereby weakening description and explanation. In many 
cases, explanations have been omitted ; in others, perhaps it 
would have been better to have done so. 

It is hoped that the more advanced teachers will find it 
possible to accompany the text-book work with laboratory 
and field study, along the line suggested in the appendix. 
The discussion of method has been systematically eliminated 
from the text, and the sole effort has been to present facts 
and furnish information ; but if this alone is put before the 
pupils, the value of the study will be very slight indeed. It 
furnishes the main story in a connected way, and supplies 
certain information ; but the laboratory and field will supplj^ 
applications and extensions of the principles, at the same 
time giving value to the study as a means of mental disci- 
pline. Merely to hear recitations from the book, will be the 
continuation of an all too prevalent habit, which in so many 
cases makes the science teaching in our secondary schools 
the weakest part of the curriculum. 

While the author has done much work in some of the 
subjects treated, particularly the ocean and the land, he 
would not wish to claim that much in the book is orio-inal. 
In reality, this book is based upon the manuscript of another 
and more advanced work, which is soon to be published as 



PREFACE. IX 

a handbook for teachers and for reference. Both of these 
represent an attempt to gather from all available sources, the 
kind of matter which it seemed desirable to include in such 
books. While in the larger work direct reference is made 
to the sources of information, it has not seemed desirable to 
do so in this case ; for the acknowledgments take much space 
and distract the attention, Avithout benetiting the pupil. 

I have had much generous assistance in the supply of illus- 
trations, particularly of photographs ; and grateful general 
acknowledgment is made here, while special mention of the 
sources is made in a list in the succeeding pages. Although 
I have received aid from many sources, there are a few which 
I must mention especially. The writings of Geikie, Dutton, 
Powell, and Gilbert, particularly the latter, have not only 
given me bodies of fact, but also inspiration, as indeed they 
have to all who are working in physiographic geology. To 
the writing-s and teachinsrs of Professors Shaler and Davis 
of Harvard University, I owe more than I could possibly 
acknowledge ; and to the latter I am under an added obliga- 
tion for his examination and kindly criticism of parts of my 
manuscript. While I acknowledge the debt which I owe 
these scientists, it must be understood that the mode of 
presentation is my own, and that I alone am responsible for 
any shortcomings which may appear. 

RALPH S. TARR. 
Ithaca, NA'., August oO, 1895. 



Digitized by the Internet Archive 
in 2011 with funding from 
The Library of Congress 



http://www.archive.org/details/elementaryphysicOOjarr 



CONTENTS. 



Part I. The Air. 



CHAPTER I. The Earth as a Planet. 



Form of the Earth .... 
The Solar System .... 

The Sun 

The Planets 

Asteroids ..... 

The Earth 

The Moon 

Comets, Shooting Stars, and Meteors 

The Stellar System 

SynunetK^' of the Solar System 

The Xebular Hy])othesis 

Verification of the Nebular Hypotliesis 



5 
6 
8 
11 
11 
13 
15 
i: 
18 
19 
20 



CHArTER II. The Atmosphere. 



General Statement 

Light 

Electricity and Mag 

Heat 

Moisture 

I'ressure . 

Effect of Gravity 

Effect of the Earth 



netism 



Rotation 



23 

25 
20 
••JO 
35 
39 
39 
39 



CHAPTER III. Distribution of Temperature. 



General Statement . 

Effect of Atmospheric Movements 



43 
44 



Xll 



C0NT£:NTS, 



Influence of Oceans 
Effect of Topography 
Seasonal Temperature Range 
Isothermal Charts . 
Daily Temperature Curve 
Temperature Ranges 
Earth Temperatures 



CHAPTER IV. General Circulation of the Atmosphere. 



General Statement .... 
Classification of the Winds 
Planetary or Permanent Winds 
Trade Winds .... 
Doldrum Belt .... 
Anti-trade Winds 
Horse Latitude Winds 
Prevailing Westerlies 
Periodical Winds .... 
Seasonal Winds 

Migrating Wind and Calm Belts 
Monsoon Winds 
Diurnal Winds 

Sea and Land Breezes 
Mountain and Valley Breezes 
Eclipse and Tidal Breezes 
Irregular Winds .... 

Accidental Winds . 
The Nature of Winds 



CHAPTER V. Storms. 



Cyclonic Storms 
Hurricanes 

Description 

Effects 

Path . 

Time of Occurrence 

Cause 



CONTENTS. 










XIU 


PAGE 


Temperate Latitude Cyclones 


. 93 


Kesemblauce to Hurricanes 












m 


Differences from Hurricanes 












95 


Effects .... 












98 


Winds .... 












98 


Anticyclones 

Cause .... 












100 
100 


Secondary Storms .... 












101 


Thunderstorms 












101 


Tornadoes and Waterspouts . 












104 



CHAPTER VI. The Moisture of the Atmosphere. 



Dew 














107 


Frost 














108 


Fog 














109 


Haze 














110 


Mist 














111 


Clouds 














HI 


Kaiu 














114 


Snow ..... 














115 


Hail 














IIG 


Distribution of Rainfall in the World 












117 


Distribution of Rainfall in the United States 












118 


Distribution of Sni)wfall 












121 


Seasonal Distribution of Rainfall . 












122 


Irregularities of Rainfall 














123 



CHAPTER VII. We.^ther .\nd Climate. 



Weather 

Tropical and Arctic . 

Temperate Latitude Weather 
Climate . 

Tropical Climate 

Temperate Climate 

Arctic Climate 

Minor Variations 

Changes in Climate 



124 
124 
125 
129 
130 
130 
132 
132 
132 



XIV 



CONTENTS. 



CHAPTER VIII. Geographic Distribution of Animals 
AND Plants. 

PAGE 

General Statement . . . i 135 

The Ocean 135 

Fresh Water I37 

The Land I37 

Effect of Temperature and Moisture 137 

Plant and Animal Habits 141 

Life Zones . 143 

The Spread of Life 145 

Barriers to the Spread of Life . ' 147 

Effect of Man . I47 



Pakt II. The Ocean. 



CHAPTER IX. Form and General Characteristics of 
THE Ocean. 

Distribution of Land and Water . 
Composition of Ocean Water . . . 
Color and Phosphorescence . 
Exploration of the Ocean Bottom . 
Methods used in Deep-sea Explorations 

Sounding ..... 

Dredging ..... 
Topography of the Ocean Bottom . 

General ..... 

The Atlantic Ocean . 

Other Oceans .... 

Topography near the Coast 
Temperature of the Ocean Bottom 
Light on the Ocean Bottom . 
Materials composing the Ocean Floor 

Mechanical Sediments 

Globigerina Ooze 

Red Clay 

Life in the Ocean .... 

Pelagic or Surface Faunas 

Littoral or Shore Faunas . 

Faunas of the Ocean Bottom . 



151 
151 
152 
153 
153 
153 
155 
156 
156 
158 
160 
160 
162 
163 
164 
164 
164 
165 
166 
166 
167 
169 



CONTENTS. 



XV 



CHAPTER X. Ocean Waves and Currents. 



Wind Waves .... 

Earthquake Waves 

Storm Waves .... 

Ocean Surface Temperatures . 

Ocean Currents 

Planetary Circulation 

The System of Ocean Currents 

Cause of Ocean Currents . 

The Gulf Stream 

The Labrador Current 

Effects of Ocean Currents 



PAGE 

174 

178 
179 
179 
182 
182 
183 
185 
187 
189 
189 



CHAPTER XL Tides. 



Nature of the Tidal Wave 

Cause of Tides 

Effect of the Land 

Other Cau.ses for Variation in Tidal Height 
Effects of Tides 



192 
192 
19:] 
198 
201 



Part TIT. The Laxd. 



CHAI'TEI{ XII. The Crust of the Earth. 



Interior Condition . 
IMovements of the Crust 
Disturbance of the Rocks 
Volcanic Action 
Rocks of the Earth's Crust 

Igneous Rocks . 

Metamorphic Rocks 

Sedimentary Rocks . 
Deposition of Sedimentary Rocks 
Consolidation of Sedimentary Rock; 
Geological Chronology . 
Age of the Earth . , 



205 
206 
207 
211 
212 
213 
214 
214 
215 
217 
218 
221 



XVI 



CONTENTS. 



CFIAPTER XIII. Denudation of the Land. 



Underground Water 

The Formation of Caverns 

Springs and Artesian Wells 

Durability of Eocks 

Weathering 

Agents of Erosion . 

Wind Erosion . 

Rain Erosion . 

Percolating Water 

River Erosion . 

Ocean Erosion . 

Glacial Erosion 
Denudation 



PAGE 

. 224 

. 226 

. 228 

. 231 

. 233 

. 238 

. 238 

. 239 

. 240 

. 241 

._ 244 

. 245 

. 246 



CHAPTER XIV. 



Topographic Features or the Earth's 
Surface. 



Continents and Ocean Basins 

Physical Geography of the United States 

Atlantic Coast Area 

The Eastern Mountains . 

The Canadian Highlands 

The Centr^a Plains . 

The Cordilleran Area 
The Drainage of the Country 
The Shore Line .... 



CHAPTER XV. River Valleys. 



General Description 

Development of River Valleys 

Adjustment of Streams 

The River Divide . 

Accidents to Streams 
Land Movements 
Climatic Accidents 
Other Accidents 



CONTENTS. 



XVll 



CHAI'TER XVI. Dkltas, Floodplains, Waterfalls, 
AND Lakes. 



Deltas . 
Floodplains 
Waterfalls 
Lakes 
Swamps . 



PAGE 

285 
288 
294 
298 
303 



CHAI'TER XVIL Glaciers. 



Cause of Glaciers . 

Alpine or Valley Glacier 

Continental Glaciers 

Icebergs .... 

Glacial Period 

Area covered by Ice 
Terminal Moraine . 
Formation of Soil . 
Formation of Lakes 
Formation of Waterfalls 



CHAPTER XVIII. The Co a 



General Statement . 
Effect of Elevation . 
Pvffect of Depression 
Effect of Sediment . 
Effect of Waves and Currents 
Effect of Plants 
Effect of Animals . 
Changes in Coast Form . 
Islands .... 
Promontories . 
Lake Shores . 
Fossil Shore Lines . 



r Line 



CHAPTER XIX. Plateaus and Moi 



Plateaus 

Mountains .... 
Characteristics of Mountains 



306 
307 
313 
31.'. 
310 
310 
319 
321 
323 
325 



>J!,. 


328 




329 




329 




330 




332 




337 




340 




343 




344 




346 




347 




348 


NTAINS. 






. 350 




. 353 




. 353 



XVlll 



CONTENTS. 



The Origin of Mountains . 
Sculpturing of iMountains 
The Drainage of Mountains 
Destruction of Mountains 



PAGE 

362 
364 
365 
367 



CHAPTER XX. Volcanoes, Earthquakes, and Geysers. 

Volcanoes .... 

Distribution 

Materials Erupted . 

Eruptions of Volcanoes . 

Form of Cone . 

Effects of Volcanic Eruptions 

Extinct Volcanoes . 

Cause of Volcanoes . 
Earthquakes . ... 

Geysers and Hot Springs 



370 
370 
371 
374 
378 
381 
381 
383 
383 
386 



CHAPTER XXI. The Topography of the Land. 

General Statement . 
Constructive Land Forms 

By Internal Forces . 

By Agents of Denudation 

By Animal and Plant Life 
Effect of Rock Structure upon Topography 



390 
392 
392 
393 
395 
395 



CHAPTER XXII. Man and Nature. 

General Statement 407 

Modifying Influence of Man 407 

Man and the Forest 409 

Influence of Nature upon Man 412 



CHAPTER XXIII. Economic Products of the Earth. 

Soil 420 

Building Stones 420 

Economic Deposits of Sedimentary Origin 422 

Miscellaneous Substances 423 



Coal 

Natural Gas and Petroleum . 
Ore Deposits .... 
Distribution of Ore Deposits . 
Mineral Wealth of the United States 



CONTENTS. 


XIX 




PAGE 




. 423 




. 425 




. 426 




. 428 


States 


. 420 



APPENDIX I. 

Meteorological InstkuiMENts, Apparatus, and Methods. 

Thermometric Records .... 
Barometric Records .... 
Measurement of Wind Direction and Force 
Measurement of Evaporation . 
Measurement of Moisture in the Air 
Study of Clouds and Sunshine 
Measurement of Rainfall 
Meteorolo<?ical Methods and Results 



431 
432 
433 
434 
434 
434 
435 
435 



APPENDIX II. 



TopoGRAPnic Maps 



437 



APPENDIX III. 



Suggestions to Teachers . 



440 



APPENDIX IV. 



Questions upon the Text . 



453 



ILLUSTRATIONS. 



DIAGRAMS AND PHOTOGRAPHS. 

FIG. 

1. Sphere and oblate spheroid 

2. Land and water hemispheres 
8. The solar system .... 

4. Relative size of sun and large planets 

5. Sun spots, 1872 

6. Relative distances of planets from the sun 

7. Relative size of smaller planets 

8. Illustration of the cause of seasons . 
0. Relative size of earth and moon 

10. Lunar craters 

11. Comet of Donati, 1858 

12. Orbit of comet of 1862 

13. Andromeda nebula .... 

14. Thickness of the atmosphere . 

15. Decrease in density of the atmosphere 

16. Passage of sun's rays through the atmospl 

17. Inclination of the sun's rays 

18. Daily change in relative humidity . 

19. Increase in temperature of descending air 

20. Deflection of air currents . 

21. Decrease in diameter on different latitude 

22. Daily temperature curves . 
2o. Irregularities of seasonal curve 

24. Seasonal temperature ranges 

25. Seasonal temperature range (New York) 

26. Isotherms for February (northern hemisphere) 

27. Daily temperature curve (summer and winter) 

28. Daily temperature range for several days 

29. Daily temperature record for several days 

xxi 



9 
12 
14 
14 
15 
16 
17 
23 
24 
26 
34 
37 
38 
40 
40 
44 
45 
49 
51 
52 
60 
61 
61 



XXll 



ILLUSTRATIONS. 



FIG. 

30. Temperature ranges, United States, 1892 . 

31. Minimum temperatures, United States, 1892 

32. Maximum temperatures, United States, 1892 

33. Daily temperature range near and above tlie ground 

34. General circulation of the globe 

35. Summer monsoons, India . 

36. Winter monsoons, India . 

37. The sea breeze 

38. The land breeze 

39. _ Effect of sea breeze on air temperature 

40. Valley breeze ..... 

41. Ideal diagram of a storm . 

42. Barometric record during passage of a hurricane 

43. Diagram of hurricane winds 

44. Map of a hurricane .... 

45. Tracks of August hurricanes 

46. Map of temperate latitude cyclone . 

47. Paths of low-pressure areas 

48. Average storm tracks, 1878-1887 (Northern hemisphere ^ 

49. Tracks of low-pressure areas . 

50. Photograph of thunderstorm . 

51. Path of thunderstorm 

52. View of a tornado .... 

53. Effect of tornado at Lawrence, Mass. 

54. Distribution of tornadoes (1794-1881) 

55. Valley fog in the Himalayas 

56. The banner cloud .... 

57. Photographs of clouds 

58. Photographs of snowflakes 

59. Damp snowfall 

60. Evaporation in United States . 

61. Monthly rainfall in the "West . 

62. Variation in annual rainfall in the West 

63. A cold wave 

64. Temperature descent during cold wave 

65. Climatic zones 

66. Near the timber line .... 

67. Above the snow line, Mount St. Elias, Alaska 

68. Effect of sunlight on mountain vegetation 

69. Arid land vegetation 

70. Arid land vegetation, Rio Grande valley 



ILLUSTRATIONS. 



XXlll 



FIG. 

71. The tropical forest . 

72. Life zones of United States 

73. Deep-sea sounding machine 

74. Deep-sea trawl 

75. Contrast between land and ocean bottom topography 

76. Cross-section of Atlantic Ocean 

77. Temperature of the Mediterranean 

78. Globigerina ooze 

79. Coral reef on Australian coast 

80. Ocean waves • • 

81. Breakers on the coast 

82. Effect of storm waves on the coast . 
8o. Normal vertical descent of ocean temperatures 

84. Tides near Hell Gate, N.Y 

85. Time and height of tides at Hell Gate . 

86. The tides at Eastport, 3Me., September, 189r5 . 

87. Height of high tide, Eastport, Me., 1893 and 1894 

88. Tidal nuid flat in Bay of Fundy 

89. Tidal rise and fall, Cape Ann, Mass. 

90. Horizontal rocks in Kansas 

91. A monoclinal fold .... 

92. Anticline 

93. Syncline 

94. Photograph of anticline, Hancock, W.Va. 

95. Photograph of anticline near Quebec, Canada 

96. Photograph of a fault in Arizona . 

97. Photograph of a fault in glacial clay, Massachusetts 

98. A dike crossing granite . 

99. Contorted limestone . • 

100. Stratified shale, near Ithaca, N.Y. 

101. Section of alternating strata . 

102. Unconformity in horizontal rocks 

103. Unconformity in inclined rocks 

104. Photograph of fossiliferous rock 

105. Mammoth Hot Springs, Yellowstone Park 

106. Diagram illustrating formation of caverns 

107. A sink hole in limestone region 

108. Stalactites in Luray Cave 
lfl9. The Natural Bridge, Va. . 

110. A sprnig on a fault plane 

111. Hillside spring ... 



PAGE 

143 

144 

154 

155 

156 

158 

163 

165 

168 

174 

175 

177 

180 

196 

196 

199 

200 

202 

203 

208 

208 

208 

209 

209 

209 

210 

210 

212 

214 

215 

216 

217 

217 

219 

225 

226 

227 

227 

228 

228 

229 



XXIV 



ILLUSTRATIONS. 



112. Photograph of an artesian well 

113. Artesian well in nionoclinal strata . 

114. Artesian well in syncline . 

115. Kock pillars in Garden of Gods, Col. 

116. The weathering of granite 

117. Effect of roots in breaking up rocks 

118. Talus in Kio Grande valley, N.M. . 

119. The formation of residual soil 

120. Sand dunes, Cape Ann, Mass. 

121. ~ Moqui pueblo. New Mexico 

122. Talus furnishing load to river . 

123. Yellowstone valley, broadening by weatheriii 

124. Boulder bed of Westfield River, Mass. . 

125. Sea cliffs on volcanic island . 
12G. Granite hill rounded by glacial action . 

127. Relief map of Eurasia . . . 

128. Section across the Atlantic and United States 

129. Relief map of North America . 

130. A deep mountain valley .... 

131. Stream rising in limestone cave 

132. Brink of Niagara Falls .... 

133. Goi'ge near Ithaca, N.Y 

134. Royal Gorge, Col 

135. Oxbow cut-off in Connecticut valley 

136. Development of the cafion 

137. Development of the canon profile . 

138. Development of old valley 

139. The Yellowstone, broadening by weathei'ing 

140. A bit of Illinois di-ainage .• 

141. A bit of West Virginia drainage 

142. Canon of the Colorado .... 

143. A broad Alpine valley .... 

144. Mountain gorge in the Alps . 

145. Diagram illustrating change in divide 

146. Diagram illustrating change in divide 

147. Diagram illustrating monoclinal shifting 

148. Diagram illustrating sudden change in divide 

149. Effect of elevation on Colorado canon . 

150. The drainage of an arid region 

151. The Great Basin 

152. Effect of glaciation on stream courses . 



ILLUSTRATIONS. 



XXV 



FIG. 

153. Delta of the Mississippi . 

154. Mode of format imi of ;i delta . 

155. An alluvial fan 
150. Floodplaiu among mountains 

157. Floodplain of a great river 

158. ^leandering of the Mississippi 

159. Meandering of the Mississippi 
1(50. Meandering of the Alississippi 

161. Falls of the Yellowstone . 

162. Taughannock Falls, N.Y. 

163. American Falls, Niagara . 
16-1. Yo.semite Falls 

165. Falls in a gorge near Ithaca, N.Y 

166. Diagram illustrating origin of Niagara 

167. River valley transformed to a lake (Adirondacks) 

168. Glacial lakes in the Adirondacks . 

169. Bird's-eye view of Niagara River . 

170. Shore lines of extinct Lake Bonneville 

171. A Florida swamp .... 

172. Ray Brook, Adirondacks 

173. An Alpine snow field 

174. Whitney Glacier, Mount Shasta 

175. The Rhone glacier .... 

176. Crevasse in a glacier 

177. Glacier, Mount Dana, Cal. 

178. Section of a glacier .... 

179. Ice cave at terminus of a glacier 

180. Forest at foot of Malaspina Glacier, Alaska 

181. A Nunatak in Greenland 

182. Icebergs in the Antarctic 

183. An iceberg in water 

184. Glacial lakes and moraine in a mountain valley 

185. Extent of the continental ice sheet in America 

186. Boulder in moraine. Cape Ann, Mass. . 

187. Bear-den moraine. Cape Ann, Mass. 

188. Boulder-strewn till soil in Maine . 

189. Glacial scratches on a pebble . 

190. Glacial lakes in Massachusetts 

191. Watkins Glen, N.Y. 

192. Sea cliff, Cape Cod, Ma.ss. 

193. Submerged valley on the coast <»f Mount Desert, Mt 



PAGE 

286 

288 

288 

289 

290 

291 

292 

292 

293 

294 

295 

296 

297 

298 

299 

300 

801 

302 

303 

304 

306 

307 

308 

309 

310 

312 

312 

313 

314 

315 

316 

317 

318 

320 

321 

321 

322 

324 

326 

328 

330 



XXVI 



ILL JJSTRATIONS. 



FIG. 

194. Ocean bar on the Texas coast 

195. Destruction of Heligoland by the ocean 

196. Lake Spit . . . . 

197. Hook, Lake Michigan .... 

198. Sea cave in granite rock, Cape Ann, Mass. 

199. Effect of dike onferm of coast. Cape Ann, Mass. 

200. Pond formed by beach barrier, Cape Ann, Mass. 

201. Crescent-shaped beach. Cape Ann, Mass. 

202. Boulders worn from headland by waves 

203. ~ Rocky beach on exposed coast. Cape Ann, Mass. 

204. Mat of seaweed between tides. Cape Ann, Mass. 

205. A mangrove swamp 

206. Salt marsh. Cape Ann, Mass. 

207. Coral reef on the Australian coast 

208. Keys on the Florida coast 

209. An atoll in the Pacific . 

210. Diagram illustrating origin of atolls 

211. The coast of Casco Bay, Me. 

212. Cliff on the shore of Lake Michigan 

213. Lagoon enclosed behind lake beach 

214. Plain in Pecos Valley, N.M. . 

215. Plain in valley of Red River of the North 

216. Taos Mountains, N.M. . 

217. Plateau near Colorado River 

218. Butte in New Mexico . 

219. Talus slope in the Elk Mountains, Col. 

220. _ Matterhoru, Switzerland 

221. A mountain park (Baker's) . 

222. Mountain gorge in the Peruvian Andes 

223. Mount of the Holy Cross, Col. 

224. Trail on Long's Peak, Col. . 

225. Mountain ridge on the Canadian Pacific 

226. Section across a mountain ridge . 

227. A bit of mountain drainage . 

228. Map of mountain drainage . 

229. Diagram illustrating the development of a mountain 

230. A mountain ridge in Colorado 

231. Vesuvius in eruption, 1872 . 

232. Surface of a recent lava flow 

233. Lake formed by a lava dam . 

234. Volcano in the Lipari Islands 



ILLUSTRATIOXS. 



XXVll 



riG. 

235. Disruption of Krakatoa .... 

236. Vesuvius, from Pompeii .... 

237. Mount Hood — an apparently extinct volcano 

238. Muir's Butte, Cal., — a recent volcano 

239. Fu.siyania, a Japane.se volcano 

240. Angle of slope of volcanic cones .* 

241. Mounts Shasta and Shastina 
212. Mate Tepee, Wyo., — a volcanic neck . 

243. Diagram illustrating the earthquake wave . 

244. Waves of Charleston earthquake . 

245. Earthquake shock in Japan .... 

246. Effect of earthquake in Japan, 1891 

247. Fault line associated with Japanese earthquake of 1891 

248. Crater of Oblong Geyser, Yellowstone Park 

249. Old Faithful Geyser, Yellowstone Park 

250. Etching of hard layer by denudation, Brazi 

251. A cliff in the Yosemite .... 

252. Cliffs in the loess of China . 

253. A wave-worn chasm, Gloucester, Mass. 

254. A rugged granite coast. Cape Ann, Mass. 

255. A sloping granite coast. Cape Ann, Mass. 

256. Effect of hard layers on topography 

257. Signal Butte, Tex 

258. Effect of tilted layers on topography . 

259. Form of seacoast in inclined strata 

260. Form of seacoast in inclined strata 

261. Ridge of hard rock, etched by denudation 

262. Topography in region of folded rocks . 

263. A part of the Adirondack forest . 

264. Deforesting of the Adirondacks . 

265. Bare rock exposed by removal of forest 
206. Model of Cumberland Valley, Penn. . 
267. Ilachure map 



PAGE 

375 
376 
378 
379 
380 
380 
382 
383 
384 
384 
385 
386 
387 
388 
389 
396 
398 
399 
400 
401 
401 
402 
402 
403 
403 
403 
404 
405 
409 
410 
411 
437 
438 



XXVlll' 



ILL US TRA TIONS. 



PLATES AND CHAETS. 



PLATK 

1. Watkins Glen, New York 

2. Isotherms for the year (world) 

3. Isotherms for the year 1892 (United States) 

4. Isothermal chart for July (world) . 

5. Isothermal chart for January (world) 
(i. Isothermal chart for July (United States) 

7. Isothermal chart for January (United States 

8. Isothermal chart of New York (year) 

9. Winds and isobars for January (world) 

10. General circulation of the Atlantic, July 

11. General circulation of the Atlantic, January 

12. Rainfall chart of the world 

13. Rainfall chart oi the United States 

14. Depths of the ocean 

15. Ocean surface temperature, Atlantic 

16. Oceanic circulation 

17. Gulf Stream ..... 

18. Co-tidal lines 

19. English Channel tides . 

20. Earth columns, New Mexico . 

21. The Bad Lands of South Dakota . 

22. Relief map of the United States 

23. Drainage areas of the United States 

24. Delaware and Chesapeake bays 

25. Drainage in glaciated region, Wisconsin 
20. White Glacier, Alaska . 

27. Distribution of volcanoes and ocean surface 

(world) ..... 

28. Marble Canon, Colorado River 

29. Navajo church, Arizona . 



facing 
furing 



facing 



facing 



PAGE 

Frontispiece 

facing 50 

. 54 

55 

56 

57 

58 

59 

70 

72 

73 

117 

. 119 

. 161 

. 181 

facing 183 

. 188 

facing 194 

. 195 

. 232 

. 247 

253 

260 

277 

283 

311 



facing 



temperatures 
facing 



370 
391 
397 



ILL US Tit A TIONS. XXIX 



ACKNOWLEDGMENT OF I L L TSTll ATIONS. 

The follo-wiiig illu.slrations are from tlie suurces indicated. In some 
cases they have been exactly reproduced, but iu others they have been made 
more diagrammatic to suit the needs of this book. Some of tlie IHustrations 
not acknov^fledged are from photographs or lantern slides, the source of 
which could not be ascertained.! 

Abbe, r. S. S. S., Annual Report for 1890, Fig. •',(',. 

Agassiz, Three Cruises of the Blake, Plate lo. 

Branner, Journal of Geology, Vol. 1, Fig. 2o(t. 

Brown, C. D. (dealer in photographs, Gloucester, Mass.), Figs. 81, 89, 203, 

204, and 254. 
Buchan, Atmospheric Circulation, Challenger Reports, Plates 2, 4, 5, and 9. 
Calvin, Prof. S., State Geologist of Iowa, Des Moines, — Photograph by the 

Survey, Fig. l."l. 
Canadian Geological Survey, Photograph, Fig. 99. 
Challenger Reports, Narrative, Figs. 78, 125, and 182. 
Chamberlin, Third Annual Report, U. S. G. S., Fig. 185. 
Diller, Bulletin 79, U. S. G. S.,^ Figs. 232, 233. 
Dunwoody, Summary of International Meteorological Observations, Figs. 20 

and 48 ; same, Profe.ssional Paper IX., U. S. S. S., Plate 13. 
Dutton, Second Annual Report, U. S. G. S., Figs. 137 and 149 ; same, Sixth 

Annual, Plate 29 ; same, Ninth Annual, Fig. 244 ; same. Monograph II., 

U. S. G. S., Fig. 136. 
Ferrel, Popular Treatise on the Winds, Fig. 34. 
Finley, U. S. S. S., Professional Paper VII., Fig. 54. 
Gannett, Thirteenth Annual Report U. S. G. S., Plate 22. 
Gardner, J. L., 2d, Boston, Mass. (Photographs by). Figs. 98, IIG,^ 117, ^ 

120, 126,3 186,3 187, 198,^ 199,^ 200, 201, 202, » 206, and 255.3 
Gilbert, Monograph I., U. S. G. S., Figs. 151, 1-54, 155, 170, 197, and 213 ; 

.same. Fifth Annual Report U. S. G. S., Figs. 212 and 217 ; .same. Annual 

Report Smithsonian Institution, 1890, Figs. 166 and 169 ; same. Geology 

of the Henry Mountains, Fig. 147. 

1 U. S. C. S., refers to the United States Coast Survey ; U. S. G. S., to the United States 
Geological Survey ; and U. S. S. S., to the United States Sig:nal Service. 

- Some of these which are referred to the Geolojfical Survey liubhcation were made from 
photographs obtained from the Survey. 

3 Also published by Sh'uler in Ninth .Vnnual Keport, U. S. G. S. 



XXX ILL US TEA TtONS. 

Greely, U. S. S. S., Professional Paper II., Plates 6 and 7. 

Griswold, L. S., Dorchester, Mass. (Photograph by). Fig. 97. 

Guyot, Physical Geography, Fig. 2. 

Hann, Berghaus, Atlas der Metedrologie, Plate 12. 

Hann, Hochstetter, and Pokorny, AUgemeine Erdkunde, Fig. 77. 

Harvard College Astronomical Observatory Engravings, Figs. 5, 11, and 13. 

Harvard College Geological Department, Figs. 215 and 231 (former, photo- 
graph from South Dakota World's Fair Commissioner ; latter, pho- 
tograph by Sommer) . 

Haynes, F. Jay, St. Paul, Minn. (Photographer), Figs. 105, 123, 139, 161, 
248, 249. 

Hellmann, Schneekrystalle, Fig. 58. 

Hill, First Annual Keport, Texas Geological Survey, Fig. 257. 

Hope, J. D., Photographer, Watkins, N.Y., Plate 1 and Fig. 191. 

Jackson Photograph Co., Denver, Col, Figs. 134, 221, 224, 237, 238, and 251. 

James, C. H., Photographer, Philadelphia, Pa., Fig. 108. 

Jukes-Browne, Handbook of Physical Geology, Fig. 195. 

Kent, Great Barrier Reef, Figs. 79 and 207. 

Kobayashi, Earthquake Observations in Japan, Fig. 245. 

Koppen, Segelhandbuch flir den Atlantischen Ozean (reproduced by Davis, 
American Meteorological Journal, Vol. IX.), Plates 10 and 11. 

Lesley, Coal and its Topography, Figs. 256 and 262. 

Levy and Co., Paris (Dealers in Photographs), Figs. 143, 144, 175, and 220. 

Merriam, North American Fauna, Bulletin No. 3, U. S. Dept. of Agriculture, 
Fig. 68; same. National Geographic Magazine, Vol. VI., 1894, Fig. 72. 

Mills, H. F., Annals, Harvard College Astronomical Observatory, Vol, 31, 
Fig. 53. 

Mills, H. R., Realm of Nature, Plates 16 and 27. 

Mississippi River Commission (Maps), Figs. 158, 159, and 160. 

Mitchell, U. S, C. S., Annual Report for 1886, Fig. 85. 

Murray and Renard, Challenger Reports — Deep Sea Deposits, Plate 14. 

Nasmyth and Carpenter, The Moon, Fig. 10. 

Newcomb, Popular Astronomy, Fig. 12. 

Newell, Eleventh Census Report on Irrigation, Figs. 61 and 62. 

Newton & Co., London, England (Dealers in Lantern Slides), Figs. 52, 55, 
71, 106, 181, 205, 209, 234, and 339. 

New York State Weather Bureau, Fifth Annual Report, Plate 8 and Fig. 25 ; 
Figures based on the records of this bureau : 18, 28, 29, 33, 42, and 64. 

Notman (Photographer), Montreal, Canada, Fig. 225. 

Pach (Photographer), New York, N.Y., Fig. 82. 

Peschels (Leipoldt), Physische Erdkunde, Plates 18 and 19. 

Pillsbury, Annual Report, U. S. C. S. for 1890, Plate 17. 



ILL rSTU. I TloyS. XXXI 

Proctor Bros. (Dealers in Pliotograpli.s), Gloucester, Mass., Fig. 80. 

Reid, National Geographic Magazine, Vol. IV., Plate 26. 

Richthofen, China, Fig. 252. 

Riggenbach (Photographs), Figs. 50 and 57 (latter from several sources). 

Ritchie, J., Jr., Boston, Mass. (Photographs by), Figs. 124 and 188. 

Russell, Fifth Annual Report, U. S. G. S., Fig. 177 ; same, Eighth Annual, 

Fig. 184 ; same, Thirteenth Annual, Figs. 67 and 180. 
Sella (Photographs; Chas. Pollock, Boston, Agent), Figs. 176 and 179. 
Shaler, Twelfth Annual Report, U. S. G. S., Figs. 107, 157, and 171. 
Sigsbee, U. S. C. S., Deep Sea Sounding and Dredging, Figs. 73 and 74. 
Smith, W. M. (Dealer in Photographs, Provincetown, Mass.), Fig. 192. 
Stoddard, S. R. (Photographer), Glens Falls, N.Y., Figs. 88, 167, 168, 172, 

193, 263, 264, and 265. 
Symons, Eruption of Krakatoa, Fig. 235. 
Todd, Bulletin I., South Dakota Geological Survey, Fig. 112. 
Trotter, Lessons in the New Geography, Figs. 127 and 129. 
United States Coast Survey Charts, Figs. 153, 194, 208, 211, 2()7, and Plate 24. 
United States Geological Survey Photographs, Figs. 66, 94, 95, 96, 119, 122, 

132, 142, 163, 174, 196, 230, 241, 242, 261, and Plate 28 ; same, Topo- 
graphic Maps, Figs. 150, 190, 228, and Plate 25. 
United States Geological Survey of the Territories (Hay den), Photographs, 

Figs. 69, 115, 121, 130, 156, 164, 219, 223. 
United States Hydrographic Bureau (Coast Pilot), Figs. 43, 44, 45. 
United States Signal Service and Weather Bureau, Figs. 30, 31, 32, 46, 47, 

49, 60, 63, and Plate 3. 
Van Bebber, Lehrbuch der Meteorologie, Fig. 41. 
Walcott, National Geographic Magazine, Vol. V., Fig. 109. 
Ward, Annals Harvard College Astronomical Observatory, \'ol. 31, Fig. 51. 
Wild, Thalassa, Fig. 21. 

Willis, Thirteenth Annual Report, U. S. G. S., Figs. 92, 93, and 101. 
Williston, Prof. S. W. , Kansas University Geological Department, Lawrence, 

Kansas (Photograph by). Fig. 90 and Plate 21. 



Part L 
THE AIR, 



ELEMENTARY PHYSICAL GEOGEAPHY. 



o^St^c 



CHAPTER I. 



THE EARTH AS A PLANET. 



Form of the Earth. — The earth i.s a spherical body com- 
posed of three different portions, — a dense central mass, which 
is probably solid, and two envelopes, the ocean and the air. 
The central part has a mnch e^reater bnlk than either of the 
other portions. In reality the form is not exactly spherical, 
for the diameter of a s[)here shonld liave the same length in 
all })arts ; but on the cartli the diameter at the e(|nator is 2C)\ 
miles longer than that at the jjoles, 
where its length is 7890 miles. 
This flattening of the poles gives 
to the earth the form of an oblate 
splieroid instead of a true sphere 
(Fig. 1). 

While this irregidarity of the 
earth was detected only after a 
series of very careful measure- 
ments, it is in reality the greatest 
on the surface of the earth; but Diagram showing a section of 

there are other and less extensive a sphere (heavy line) and an 

oblate spheroid (dotted line). 

irregularities, which are much 

more noticeable. These are of two kinds, — continents and 
mountains. The surface rises and falls in a series of great 
wave-like irregularities, which form the continents and ocean 

3 




PHYSICAL GEOGRAPHY. 



basins. On the continents, and occasionally in the oceans, 
the surface rises along relatively narrow lines into a series 
of high mountain ridges. Although these, are the greatest 
elevations on the earth*s surface, and therefore attract our 
attention, they are really very small irregularities when com- 
pared Avith the continents of which they usually form a small 
portion (Fig. 128). 

Considering the sea level as 0, the highest point on the 
earth is about 29,000 feet in elevation. Depressions of over 
25,000 feet are found in several places in the ocean beds. 
The total range in elevation between the iiighest mountain, 
and the greatest ocean depth is about 57,000 feet. It can be 
readily seen how small tliis is in comparison with the earth 
as a whole, when we remember tliat the diameter of the earth 
at the equator is -11,847,192 feet. Upon a globe of ordinary 
size they could not be shown on true scale. Although there 
are points on the land whose height is greater than the 
deepest known parts of the ocean, the average deptli of 
the ocean, which is about 12,000 feet, is much greater than 
the average height of the land, which is approximately 2500 

feet (see Chap. XIV.). 
The greater part of the 
Avater on the earth's sur- 
face is accumulated in the 
broad hollows l)etween 
the continents. The sur- 
face of this water mass is 
much greater in area than 
that of the land (Fig. 2), 
the proportion being 1 of 
land to 2. 6 of water (roughly 3:8). Late calculations give the 
area of the land as 142,000,000 square kilometers, and of the 
water as 368,000,000 square kilometers. The total volume of 




Fig. 2. 
Land and water hemispheres. 



THE EARTH J.s' A PLANET. 



5 



the Avatcr of tlic oceans is esliiiuited to be l,o4T,S74,85() (•ul)ie 
kilometers. 

There are othei' smaHer irregularities on the-surl'ace of the 
earth, and luaiiy minor [)e('uliarities, somi; of which are dis- 
cussed in the later eluipters. Surrounding' the earth is a. 
gaseous envelope, the atmosphere, which extends to an 




Fn;. :;. 

'J'lie solar systcin. sliowiiin llic relative (lislaiices Iroiii tlie sun, the ilireetioii (i|| 
revolutions, relative size of tJie orbits, ami tjie iiuinlier of satellites. 



unknown distance, hut which at a lieight of iive or six ndles 
from the sui-face is very niueh rariiied. 

The Solar System. — The earth is one of .several bodies 
wduch together form the solar system. They are a family of 
bodies bound together by the tie of gravitation and engaged 
in a series of movements around a central Ijody, the sun 
(Fig. o). In the solar system there are five classes of 



6 PHYSICAL GEOGRAPHY. 

bodies. In the center is the sun, the largest of all, and the 
one upon which the others depend more than upon any other 
member. The second class of bodies is that of the planets, 
of which eight are known. These all revolve around the 
sun in orbits Avhich are nearly circular, but not exactly so, 
being in reality, ellipses with the sun at one of the foci. 
The third class of bodies is that of the satellites, of which 
the moon is an example. Most of the planets have satellites, 
which are always much smaller than the planet about which 
they revolve. The earth has but one moon, but some of the 
planets have several. Twenty moons have already been 
discovered, of which all but three belong to the outer group 
of planets, Jupiter, Saturn, Uranus, and Neptune. A fourth 
group of bodies in the solar system is that of the asteroids, 
of which about 400 are now known. These small planets 
revolve about the sun in the space between the orbits 
of Mars and Jupiter. Aside from these members, there is a 
fifth group of irregular bodies, the comets and meteors, 
which move in a manner different from that of the other 
members of the solar system. 

The Sun. — The central and largest member of the solar 
system, tlie sun itself, unlike the planets, is so constituted 
that it sends out into space a form of energy which produces 
both light and heat. It is the source of nuich of the energy 
which finds expression upon the surface of the earth in the 
forms of light, heat, and life itself. This immense body is 
fully 92,750,000 miles distant from the earth. 

Since the sun is able to emit rays which produce heat, we 
know that it must be a hot body ; but there is as yet no 
means of telling what its temperature is. Owing to the way 
it effects the movements of the several members of the solar 
system, it is known that the materials composing the sun are 
not so dense as the solid part of the earth. It seems quite 



THE EARTH AS A PLANET. 



certain that at least a large part of the sun is in the form 
of gas. By means of the instrument known as the spectro- 
scope., we have learned much concerning the actual composi- 
tion of the sun. By this instrument it has been found that 
many of the, elements known on the earth exist in the sun 
in a gaseoiis form. 

Since we know very little about the condition of the 
earth on which we live, it is hardly to be expected that our 
knowledge of a body so distant as the sun would be very 
accurate. Still the studies which have been carrietl on by 
means of the telescope have revealed the fact that there are at 
least three quite different 
parts to the sun. These 
are the corona., which is 
outermost, the chromo- 
sphere., and the photosphere, 
the latter being the densest 
part. It is the portion 
from which the light and 
heat are emitted ; and 
from its surface the diame- 
ter of the sun is about 
860,000 miles (Fig. 4). 
Above the photosphere 
comes the chromosphere, 
which appears to be the 
true atmosphere of the sun. It consists mainly of glowing 
hydrogen gas ; but in its lower portions many metals, such as 
iron, are known to exist in the form of gas. It is in violent 
connnotion, as if in eruption ; and the photosphere itself also 
presents signs of violent activity. Extending to a distance 
stnnetimes as great as 300,000 miles above the surface of the 
sun, is the corona-, the character of which is not understood. 




Fig. 4. 
Diiigram to show the rehitive size of the 
sun aud the largest planets. Drawn uu 
true scale. 




8 PHYSICAL GEOGRAPHY. 

Certain dark bodies known as sun spots (Fig. 5) appear 
upon the surface of tlie sun and move across its face until 

,they disappear on the opposite 
side, being carried around by the 
rotation of tlie sun. Their origin 
is not known, but they appear to 
liave an influence upon the earth 
in at least two ways, one upon 
atmospheric electricit}^, the other 
upon certain climatic features. 

Sun spots,' 1872. . '^^^^ ^^"^ ^^ engaged in two mo- 

tions. It rotates, as do all the 
larger bodies of the solar system ; but the period of rotation 
is not exactly known, though it is somewhere between 25 
and 26|^ days. Strangely enough, the period of rotation 
appears to vary according to the latitude. The second mo- 
tion is one in which the entire solar system is engaged ; but 
the amount and exact nature of this is not known. The sys- 
tem is moving through space at an unknown rate, toward 
the constellation Hercules. 

The Planets. — Mermiry, the smallest of the planets, is nearest 
to the sun, on the average being about 35,750,000 miles from 
it (Fig. 6). Tlie diameter is a little more than one-third 



Mara Jupiter 

|H4i- 



■V y Ea,th 

Fig. G. 
Diagram to show the relative distances of the various planets from the sun. 

that of the earth (or 2992 miles), and it rotates on its axis 
in about 24 hours, while it revolves around the sun once 
in about 88 days. We know little concerning the condi- 
tions on this planet. 



THE EARTH AS A PLANET. 



9 




Fk;. 7. 
am to show the rela- 
tive size of the smaller 
planets. 



The next body cnitside of Mercury is J^e)nis, the most 
brilliant of planets. It is almost the same size as the 
earth, being in reality abont '250 miles less in diameter 
( 70(10 miles) (Fig'. 7). Some observers 
think that they have detected a rotation 
w ith a period of a little more than 24 
hours; but this is doubted by most 
astronomers. The period of revolution 
is eonsiderably less than ours, or about 
'2'lo days. It appears (piite certain that 
tiiere is an atmosphere upon this planet, 
and so far as we can tell, it closely 
resembles ours. No satellite is known Dia^i-f 
to exist. 

Outside of the earth, which is the 
next planet in the solar sj'stem, comes Mars, which next 
to Mercury, is the smallest of the planets, having a diameter 
of but little more than 4200 miles. Its time of rotation is 
a little over 24^ hours, and its revolution about the sun 
is accomplished in nearly 687 days. Its mean distance from 
the sun is 141,000,000 miles. The axis of Mars is inclined 
about 27° to the plane of its orbit, which is about 4° more 
than the inclination of the earth's axis. There are two tiny 
satellites, one less than 10 miles in diameter, the other 
[)erhaps twice that size ; and the latter is not more than 
4000 miles from the surface of the planet, about which 
it revolves in a period of 7 h. 39 m. 

Jupiter, the largest of planets (Fig. 4), has a mass greater 
than that of all the others combined, the mean diameter being 
al)out 86,000 miles; but the diameter at the equator is fully 
5000 miles greater than that at the poles. The volume 
of Jupiter is about loOO times that of the earth. On the 
average, the distiince from tlie sun is al)out 480,000,000 



10 PHYSICAL GEOGBAPHY. 

miles, and it takes nearly 12 years for it to make a revolu- 
tion about the sun. The time of rotation is a very little 
over 9 h. 55 m. 

It is evident that what we see with the telescope is not 
the surface of the planet, but a dense atmospliere of some 
form of vapor. Therefore we have no means of knowing- 
what the actual condition of Jupiter is, though we may infer 
that the planet is still heated, and that the clouds which 
we see are the result of this heated condition. Four moons 
revolve about Jupiter, the most distant being 1,162,000 miles 
from the planet, while the nearest is only a little farther 
away than our moon is from us. 

Next beyond Jupiter is Saturn, the second largest of the 
solar planets. Its distance is 881,000,000 miles from the 
sun, around which it revolves in about 29|- years, while it 
rotates upon its axis in 10 h. 14 m.^ This planet has eight 
moons ; but the most remarkable feature connected with it, 
is its surrounding pair of flattened rings, whose inner diame- 
ter is 100,000 miles. The telescope 1ms not yet definitely 
revealed the nature of these rings. 

As the distance from the earth increases, our knowledge 
of the members of the solar system becomes less accu- 
rate. Hence, since its mean distance from the sun is fully 
1,771,000,000 miles, Uranus is scarcely known. It revolves 
about the sun once in 84 years, but its period of rotation 
is not known. There are four satellites. 

Until 1846 no other large planet was known; but as a 
result of prediction, I^eptune was discovered in that year. 
The discovery of this planet is one of the most remarkable 
proofs of the accuracy of the theory of gravitation; for it 

1 It will be noticed that as the distance from the sun increases, the time 
required for a revolution also increases, while the period of rotation rapidly 
decreases. 



THE EARTH AS A PLANET. 11 

was determined l)y irregularities in the movement of Uranus, 
that another phmet must exist outside of its orbit; and after 
careful calculations, the place where this planet could be 
found was predicted, and Neptune was discovered at a mean 
distance of 2,775,000,000 miles from the sun. One moon 
has been detected. 

Asteroids. — In the year 1801, a small planet known as 
Ceres was discovered in the space between Mars and Jupiter. 
Since that time about 400 other smaller bodies have been 
found in the same general region. In no cases have these 
,mall planets a diameter greater than 520 miles, while the 
smallest that have been discovered have diameters of less 
than 40 miles. Tlieir movement through space is some- 
what irregular; and there have been many speculations con- 
cerning their origin, though as yet no satisfactory explana- 
tion has been advanced. 

The Earth. — While cold at the surface, we have many 
reasons for believing that the interior of the earth is highly 
heated. Proof of this is found in the facts that at the 
surface, volcanoes emit quantities of molten rock which come 
from below, and that in all deep mines and well-b<n-ings the 
temperature of the rocks is found t(^ increase at a moderately 
uniform rate, on the average 1° for about every 50 or 60 
feet of descent. If this rate of increase continues, the rocks 
at a depth of less than 100 miles are so hot that they would 
be molten under the conditions which exist at the surface. ^ 

It was once believed that the interior of the earth was in 
a molten condition, and that the solid surface was merely 
a crust resting upon this liquid sphere; but many facts now 
lead us to the belief that the interior is at least as rigid as 
steel. The proof of this is mainly astronomical, and cannot 
be adequately stated here. At present we are forced to the 
belief, that although highly heated, the rocks in tlie interior 



12 



PHYSICAL GEOGBAPIIY 



of the earth are prevented" from melting by the great pres- 
sure of the overlying layers; and by this theory we are able 
to satisfactorily account iov all of the plienomena that 





Day .luring Spi-inj 

Sun li(clit just touulies 

north & south poles 



SU/j, 





Nortliern "Winter 

Sun just reaches 

the Arctic Circle 

No day 



Fig. S. 
Diagram illustrating the cause of seasons. 

formerly seemed to demand the explanation of a liquid 
interior. 

The earth is engaged in a number of movements in space. 
It revolves around tlie sun in 365 days and 26 minutes, in an 



THE EARTH AS A PLANET. 13 

orbit which is nearly a circle; but instead of being actually 
a circle with the sun at its center, the orbit is really an 
ellipse with the sun at one of the foci. Therefore, in the 
course of its revolution, the earth is at one time farther from 
the sun than in the opposite season, the distance now vary- 
ing between 91,000,000 and 91,000,000 miles, with an average 
distance of about 92,750,000 miles. 

During the revolution, tlie earth rotates about one of its 
diameters, which we call the axis, and this rotation occu- 
pies a little less tlian 21 hours (23 h. 50 m.), or one 
day. This rotation causes the familiar alternation of day 
and night; and if tlie earth's axis were at right angles to the 
plane of revolution, the day and night would be equal in 
length ; but since it is inclined to this plane at an angle of 
23° 27', the relative length of day and night varies from 
day to day. Indeed, the seasons themselves depend upon 
this inclination of the poles (Fig. 8); for in the course 
of a revolution, the pole is always pointed toward a certain 
part of the heavens ; and as the earth moves al)out tlie sun, 
the northern hemisphere alternately faces and is turned away 
from the sun. When turned toward the sun, the summer 
season is caused, and when turned away from it, the winter 
season results, because the solar rays then fall less vertically 
upon the hemisphere, and the length of the day is shorter. 
Between these two opposite seasons we liave spring and 
autuuni. 

The Moon. — This, the nearest to our earth of all the 
heavenly bodies, lias an average distance of about 210,000 
miles, and a diameter of 2160 miles (Fig. 9). Since the path 
of the moon about the earth is an ellipse with the earth at 
one of the foci, the distance varies; but it is rarely more 
than 253,000 miles nor less than 227,000 miles distant. 
When farthest, from the earth it is said to be in Apogee, 



14 



PHYSICAL GEOGRAPHY 




Fig. 9. 

The relative size of 
eartli and moou. 



and when nearest in Perigee ; and once in every revolution 

Apogee and Perigee are reached. 

Aside from those it makes in company with the earth, its 

two important movements in space are a revolution around 
the earth and a rotation about an axis, both 
of these movements occurring in the same 
period of time, or 29^- days. Therefore 
one side of the moon is never seen from the 
earth. Also, as a result of this condition, 
tlie length of the lunar day is 29| of our 
days ; and therefore at the lunar equator 
the sun shines steadily for nearly 15 days 
and is absent an equal length of time. 

Under these conditions the surface of the moon is warmed 

during the long day, and at night becomes cooled down to 

temperatures which . „„ 

are perhaps as low as [ 

- 200°. I ^ I 

There is no atmos- ; . - ' 

phere and no ocean 

on the moon ; and 

the only change upon 

the surface seems to 

be that between con- 
ditions of heat and 

cold, and light and 

darkness. It does not 

emit a perceptible 

amount of radiant 

energy, and the light from the moon is reflected sunlight. ^ 

As a result of the careful telescopic study of the moon, 

1 Direct light from the sun is 600,000 times as strong as that which is 
reflected from the moon. 




Fig. 10. 
Lunar craters, the largest being Gassendi. 



THE EARTH AS A PLANET. 



15 



astronomei's liave been iil)le to map many of the details of lunar 
topography, with consi(leral)le accuracy, and even to measure 
mountain heights. While there are other striking topo- 
graphic features, the most notable thing about the lunar land- 
scape is the great number of crater-like nu)untains, Avhich bear 
a certain resemblance to the volcanoes on the earth's surface, 
excepting that many of them are of immense size (Fig. 10). 
Comets, Shooting Stars and Meteors. — Aside from those 
described, which may be considered the normal mendjers of 
the solar system, there are other heavenly bodies which 

do not appear to be regvlar parts of the system, llie 

strangest of these are comets. Some 500 of these have 

been recorded as visil)le to the naked eye ; and in addition, 

over 200 have been detected by the aid of the telesc^ope, some 

of these being millions of miles in length. When near the 

sun, they usually have a relatively dense head and a vaporous 

tail, through which stars are visible (Fig. 11). Some have 

regular elliptical orbits, and 

their time of appearance can 

be closely calculated ; but 

the orbits of others are ap- 

parentlt/ parabolas, so that 

if they ever return to the 

solar system, it is only after 

long periods of time have 

elapsed, and after having 

made a journey far beyond 

the outermost limits of the 

solar system. Perhaps these may be mere wanderers through 
space, whicli after one visit to the solar system, depart never 
to return again. What they are, whence they came, whither 
they are going, or what relation they bear to the solar sys- 
tem, is stdl an unsolved mystery. 




Fig. 11. 
Coet of Donati, 185S. 



16 



PHYSICAL GEOGBAPHY 



Comets have an added" interest to us, from the fact that 
some slwotlng stars and meteors seem to be remnants of 
comets, which at some former time have crossed the orbit 
of the earth. Thus the November meteorites are due to the 
fact that in its movement around the sun the earth en- 
counters particles that are left in the trail of a comet (Tem- 
pel's) whicli has a period of revolution of about thirty-three 
years ; and the August meteors (Fig. 12) appear to have 
a smiilar origin. 

Meteors and shooting stars (meteors are large shooting 
stars) enter the earth's atmosphere at a high rate of speed, 

and are burned up 
. o,\ of Aufiusf Mch prs lu tlic luglier hxycrs 

of the atmosphere, 
often at an eleva- 
tion as great as 100 
miles from the sur- 
face of the earth. 
This burning is 
the result of fric- 
tion with the air, which produces a high heat, because in 
addition to the movement of the meteor, there is often 
added the motion of the earth itself, which is about 98,000 
feet a second. Hence in small l^odies, the burning is almost 
instantaneous ; but some of the larger meteors pass entirely 
through the atmosphere, and reach the earth's surface. 

A study of these rather rare meteorites, reveals to us the 
very interesting fact that no hew element exists in them ; 
and tlierefore we may fairl}^ conclude that the elements 
composing comets are the same as some of those which make 
up the earth's crust. In watching the heavens at night, 
scarcely an hour can pass without noticing shooting stars ; 
and since the same would probably be true of the day if we 




Fig. 12. 
Orbit of the second comet of 1862. 



rilE EARTH AS A PLANET. 



17 



could then see them, we ('oneliule that there are immense 
iiuml>ers of tliese bodies in the spaci! through which tlie earth 
travels. 

The Stellar System.— Far away in space, mauy times 
farther than' the sun is from us, innumerable stars are 
scattered. Already many thousands are known, and it is 
estimated that over 30,000,000 are visible with the telescope. 
Like the sun, they emit an energy which produces hoth 
light and heat ; and it is very probable that many, if 
not all, have planetary bodies revolving about them. 
One satellite, that l)elonging to Sirius, has already been dis- 
covered ; and some double 
stars are known to be re- 
volving about a common 
center of gravity. The 
distance Ijetween the stars, 
and even between the earth 
and the nearest stars, is im- 
mense, and in most cases in- 
calculable. If each star is 
a sun with accompanying 
planets, and it' each of these 
suns is as far from its neai'- 
est stellar neighbors as we 
are from ours, the immensity 
and grandeur of the system 
transcends our imagination. 
The stars are arranged in 
a- disc-like l)elt, the greatest 

diameter of wliich is in the direction of the ^Tilky Way. 
At right angles to this there is a zone of abundant nelndau 
(Fig. 13), although these strange bodies are not absent from 
other parts of the heavens. Some have conjectured that 




Fid. i;^. 

Ardroiueda nebula, from a drawinj: 



1^8 PHYSICAL GEOGRAPHY. 

nebulffi are other stellar systems, so distant from ns that 
the individual members cannot be separated by our tele- 
scopes ; but the spectroscope seems to show that they are 
bodies of glowing gas, and this has an important bearing 
upon the nebular hypothesis, which we soon discuss. One 
very important thing concerning both stars and nebuh«, is 
that the spectroscope has detected in them many of the 
elements which we find upon the earth. 

A -question of very deep interest, is whether the stars form 
a great system in which the individual members are inter- 
related, as is the case among the members of the solar 
system ? Unfortunately, in the present state of science, we 
are unable to return a definite answer to this question. 

Symmetry of the Solar System. — In theorizing upon a 
basis of known facts we must confine ourselves to the solar 
system ; ajid it is interesting to note the wonderful symmetry 
of arrangement and the beautiful order which exists here. 
Throughout the entire system, the law of gravitation prevails 
and governs the movements of all the bodies, each member 
attracting the other in direct proportion to the product of 
the masses and inversely proportional to the square of the 
distance. The regular members of the system are all nearly 
spherical, and they rotate about an axis and revolve in an 
orbit which is nearly circular. In direction of rotation and 
revolution there is a marked uniformity, as there is also in 
the plane of revolution. 

All of these regularities of behavior, take place notwith- 
standing the fact that immense distances separate the various 
bodies, and that this space is practically void. We can form 
no accurate conception of these immense distances ; but the 
following quotation from Newcomb's Astronomy furnishes 
some idea of this : — 

"To give an idea of the relative distances, suppose a 



THE EARTH AS A PLANET. 19 

voyan'iT tlir()Ui;'li the ('elcstial s})accs could traAcI from tlie 
sun to the outerniost planet of our system in twenty-four 
liours. So enormous would be his vtdoeity, that it wonld 
t-arrv him aej'oss tlie Atlantic Oi-ean, from New York to 
Liverpool, in less than a tenth of a seeond of the clock. 
Starting from the sun with this velocity, he would cross the 
orltits of the inner planets in rapid succession, and the outer 
ones more slowly, until, at the end of a single day, he would 
reach the confines of our system, crossing the orbit of Nep- 
tune. But, though he passed eight planets the first day, he 
would pass none the next, for he would have to journey 
eighteen or twenty years, without diminution of speed, 
before he would reach the nearest star, and would then have 
to contiiuie his journey as far again before he could reach 
another. All the planets of our system would have vanished 
in the distance, in the course of the first three days, and the 
sun would be but an insignificant star in the firmament. 

The sun in the center of the solar system is a true star, in 
many respects like the others which dot the firmament. 
This being the case, may we not fairly speculate as to the 
possibility of other Avorlds and systems like our own, far 
away in space, even to the outermost limits which can l)e 
reached by the human vision ; and if this be so, how vast is 
the universe, and how insignificant the small cold body of 
matter upon Avhich Ave dwell I 

The Nebular Hypothesis. — Before many facts concerning 
the universe were known, the philosopher Kant proposed a 
hypothesis to account for the origin of the solar system : and 
later, Herschel and Laplace proposed an explanation which 
in many respects was like tliat of Kant. We know this 
explanation under the name of the nebular hypothesis. 

By this it is assumed that the s[)ace occu})ied by the 
members of the- solar system, and probably even to a con- 



20 PHYSICAL GEOGRAPHY. 

.si(leral)le distance l)ey()n(l tlii.s, was occupi(3(l by a nelnilous 
mass of highly heated vapor. It is one of the hiws of nature 
that radiant energy passes from warmer to colder bodies, and 
that by this radiation a contraction and condensation neces- 
sarily follow. This nebulous mass, composed of all the ele- 
ments which now enter into the composition of the various 
members of the solar system, during the process of cooling 
separated into rings which were the parents of the several 
planets. As the mass lost lieat and Ijegan to condense and 
contract, tlie materials began to accumulate about some 
denser part of these rings, the accumulations alxwt tliese 
denser portions l^eing determined by the fact that gravita- 
tive action was stronger there than elsewhere. 

As a result of this accumulation about centers, the original 
nebulous mass became broken up into several smaller masses 
of similar nature ; and by a continuation of the process other 
rings were thrown off, out of which the satellites were 
formed. Original motion about a central portion of the 
nebula has naturally been inherited and is now indicated 
l)y the movements of the bodies in the solar system. The 
cooling of these bodies is still in progress, and different 
meml)ers of tlie system have reached different stages. 

Verification of the Nebular Hypothesis. — While we cannot 
state that this theory is definitely proven, many facts point 
to its truth as a general explanation of the solar universe. 
For instance, it would account for the fact that the planets 
move about the sun in a common direction, and that the 
planes of revolution are nearly the same in the different 
planets (the inclination in no case being more than a few 
degrees) . This similarity also extends even to the satellites ; 
and the rotation of the l)odies whose rotation has been 
determined has the same kind of uniformity. All of the 
orbits of the members of the solar system are ellipses 



THE EAJiTTT ,IS' A PLANET. 21 

:il»|)i'<iacliin^- a cii'clc. Tliis tdgellicr with the iiiiil'onn action 
of gnivitatioii suggests a, coiiiinon origin. 

The fact that all the bodies regularly belonging to the 
solar system nre nearly spherical in form is suggestive; and 
this form can readily be accounted for if the bodies were 
once li(i[uid. A former li(}uid condition is indicated by the 
fact that those bodies which are well known, all have a 
largei" diameter at the equator than at the poles ; and this is 
what would result from centrifugal action in a liquid sphere. 
Then also, signs of heat are })lainly seen in some of the mem- 
bers of the solar system ; and in the smaller bodies these 
signs are less api)arent. Thus the sun is highly heated ; 
Jupiter, Saturn, and other of the outer })lanets show signs 
of considerable heat ; the earth is cold at the surface, and 
hot in the center ; INIars, Venus, and Mercury are cold at the 
surface ; and the moon appears to be entirely cold. 

U})on the nebular hypothesis, we should expect that the 
density of the members of the solar system would increase 
from the outer bodies toward the center ; and this actually 
is the case, the only exceptions being the easily explained 
cases of Saturn and the sun. There are other reasons for 
believing in the nebular hypothesis. So far as we may 
judge from the results of spectroscopic study and from 
the examinations of meteorites that have fallen upon the 
earth, the bodies in the solar system are composed of the 
same elements as those which make the earth ; and tliis sug- 
gests that they liave been made from the same original mass. 

Far away in space, beyond the solar system, we even find 
nebulous masses of gas which are exactly like those out of 
which the solar system is believed to have been made ; and 
in some of these nebula; the condensation into planetarj' 
bodies appears to l)e in progress (Fig. 13). Nearly every 
gradation has been found between this kind of nel:)nla and 



PHYSICAL GEOGjRAPHT. 



tliiit which is apparently one mass of g-h)wii]o- gas. It is 
not improbable that even now other worlds are in process 
of formation in the far distant regions of space. 



KEFERENCr; BOOKS. i 

Newcomb. — Popular Astroxomy (school edition). Harper Brothers, New 
York. Seventh edition, 1894. 8vo. Published also in larger form. 
School edition, .$1.80 ; larger book, .$2.50. (General and quite elementary.) 

Lockyer. — Elementary Lessons in Astronomy. Macmillan & Co., New 
York. 8vo. .$1.25. (General and elementary.) 

Chambers. — Handbook of Descriptive and Practical Astronomy. Mac- 
millan & Co., New York. Fourth edition, 1889. 8vo. Three volumes. 
Vol. I., $5.25 ; Vol. II., $5.25 ; Vol. III., $3.50. (Large and comprehen- 
sive.) 

Proctor and Ranyard. — f )ld and New Astronomy-. Longmans, Green, & 
Co., New York, 1892. 8vo. .'^12.00. (Complete and well illustrated.) 

Young. — The Sun. International Scientific Series. Appleton & Co., New 
York, 1893. 12mo. -$2.00. 

Lockyer. — The Chemistry of the Sun. Macmillan & Co., New York, 1887. 
8vo. .'f4.50. 

Nasmyth and Carpenter. — The Moon. Murray, London (Scribner, New 
York agents), 1885. 8vo. $8.40. (Many remarkable photographs.) 

Nelson. — The Moon. Longmans, Green, & Co., New York, 1876. 8vo. 
$10.00. (Well illustrated.) 

Lockyer. — The Meteoritic Hypothesis. Macmillan & Co., New York, 
1890. 8vo. $5.25. (Suggestion of modification of the nebular hypothesis.) 

Scheiner (translated by Frost). — -A Treatise on Astronomical Spec- 
troscopy. Ginn & Co., Boston, 1894. 8vo. $5.00. 

^ In giving the publisher's name, the real publishing house is often not mentioned. 
Wherever possible American houses are given, and since some of these act as agents for 
European houses, the name of the arjent will at times appear in the place of the English 
publisher. 



CHAPTER IT. 



THE ATMOSPHERE. 

General Statement. — Outside of the solid earth, and ex- 
tending to a distance of several hundred miles above it, is a 
gaseous envelope, which we 
know as the atmosphere (Fig. 
14) . Its density decreases from 
the surface of the earth toward 
the upper portions ; and at a 
height of five miles it is very 
much rarefied. That it ex- 
tends to this great height is 
shown l)y the fact that meteors 
become white hot by friction 
with it, even at a greater dis- 
tance than this from the earth. 
Fully one-half of the mass of 
the atmosphere is within four The earth with its atmospheric euvel- 

" L ^,pg^ drawn to scale. 

miles of the surface of the 
earth ; and two-thirds of it is within six miles of the surface 

(Fig. 15). 

The atmosphere is composed almost entirely of two gases, 
nitrogen and oxygen, in the proportion of about 7*.) to 21. 
These o-ases are not in chemical combination, but are 
mechanically mixed. Nitrogen is a very inert element, while 
o.vi/t/en is active in the production of many changes, and trom 




Fig. U. 



24 PHYSICAL GEOGRAPHY. 

this standpoint the nitrogen- of the air may be considered as 
an adulterant of the active oxygen. In addition to these 
gases there is a comparatively sinallamount (about 0.08 per 
cent) of carboiiic acid gas,' the percentage varying some- 
what according to the location. Its percentage increases in 
the vicinity of volcanoes and large cities.^ 

Beside these three gases there are minor and variable quan- 
tities of other substances ; but of these, only two, water vapor 
and dust particles, are of sufficient general importance for 
consideration here. The term "c^ws-^" includes a great 



Fig. 1-) 
Di.igi.im to illiistiate decrease lu deiibity of the .itmospliete. 

variety of substances, such, for instance, as microbes, smoke 
particles, and true dust, Avhich is borne into the air by the 
winds. It seems certain that dust is of much importance in 
the formation of rain and fog. 

Water is readily evaporated, and hence at all times there is 
some water vapor in the air; but the amount depends upon a 
variety of circumstances, chiefly the temperature of the air 
and the presence or absence of bodies of water. The higher 

1 While this book is in preparation, the discovery of a new constituent of 
the atmosphere is announced. Tliis, which is called argon, may be a new 
element, but it is now too early to state anything definite about this sub- 
stance. 



THE ATMOSl'llEUE. ^O 

the teniperatiire, the greater the rate t.f evai)()ratinii ; l.ut 
even at temperatures beh)W freeziiig--i)i)iiit small (luaiitities 
of water vapor may he present. 

The atmosphere is of great importanee in many respeets. 
It distributes the Ug-ht whieh eomes to us from the sun. It 
is set in motion by tlie sohir energy, and by this means dis- 
tributes heat over the eartli. As a result of the effeet of 
solar heat upon the atmosphere a great variety of phenomena, 
sueh as winds, storms, elouds, ete., are produeed. These 
cause many changes upon the surface of the earth, and 
directly and indirectly the air makes the earth a place tit for 
habitation. 

Light. We obtain light from several sources, — tlie sun, 

the stars, and the ukjou and planets. Light from the latter 
source is merely reflected sunlight, and it is small in amount. 
That which comes from the stars is radiated from them 
directly, but it also is insignificant in comparison with that 
received from the sun. 

Solar light, when it reaches the lower layers of the atmos- 
ohere, produces the impression upon the eye whieh Ave know 
as white; but there is reason to think that it has a bluish 
tinge before its passage through the air. According to the 
undulatory theory, light passes through the space between 
us and the sun at a very rapid rate in the form of a series of 
waves of ether. It is made up of many waves of different 
lengths, the cond)ination of which gives white. When 
separated, these appear as different colors, and in the raiidx.w 
we recognize seven priuiary colors with intermediate tints. 
The violets and blues have the shortest vibrations, and the 
yellows and reds the longest. As a result of the effect of 
the atmosphere upon these parts of white liglit many optieal 
})lienomena are produced. 

If there were Jio atmosphen', the earth's surhiec would be 



26 



PHYSICAL GEOGRAPHY. 



illuminated only where the direct rays of the sun fell. The 
atmosphere serves to diffuse light and to render the darkness 
of shadows less intense. . This diffusion of light in large 
measure depends upon the ^amount of solid or liquid impuri- 
ties in the air. In its passage through the air, certain of the 
rays are diffused more readily than others by the process of 
sdective scattering. It is usually those with the shortest 
Avave lengths that are thus scattered; and hence it is that 
the-, sky is ordinarily blue. The intensity of the blue is 
greatest when dust impurities are least abundant, as is the 
case when the air is clear and dry. If dust particles happen 
to be very abundant, even the coarser rays of yellow light 
may be scattered ; and under rare conditions of very smoky 
air the entire sky may assume a brassy color. Since the 
light is obliged to travel through a greater distance of air 
near the time of sunset than in midday, the color of the 
western sky in the late afternoon is often j^ellow, while that 

of midday was a 
dull hazy blue (Fig. 
16). 

Among the most 
beautiful of light 
effects in the atmos- 
phere is that of the 
sunset colors., which 
are due to the scat- 
tering of the waves 
have the 
As 
a result of this the 
coarser yellows and reds come to us, the reason for the scat- 
tering being the fact that the light at the time of sunset and 
sunrise passes through a great thickness of air, and lience the 




Fig. 16. 
Diagram to show that the sun's rays pass thi'ough a ,„i, • „ i, 
greater thickness of atmospliere at sunset and su^n- 
rise than at midday. (Thickness of atmosphere smaller leugtht 
greatly exaggerated). 



THE ATMOSPIIEUE. 2T 

waves encounter a greater number of dust particles. When 
the atmosphere contains much dust, the morning and evening 
colors are often very hitense, hut an increase in the quantity 
of dust beyond a certain point tends to dull the tints. With 
chnuls in theiunizon at sunset or sunrise, these colors of red 
and yellow are often reflected in infinite variety of shade 
and tint. Other phenomena, such as the twilight arch, the 
glow and the afterglow, are not easily explained in a few 

words. 

Another property of light is that of reflection, and as a 
result of this many interesting optical effects are produced. 
The light of the moon depends upon the reflection of sun- 
light from its surface. The earth also reflects light, and 
this is one of the reasons for the illumination of places that 
are in the shadow of the direct rays of the sun. Other 
places which are illuminated reflect some of their light to 
the parts that are in shadow. Clouds also reflect the light 
of the sun ; and on summer days, when great banks of 
clouds rise high in the air, their surfaces are brilliantly 
illuminated and l)eautiful cloud effects are produced. 

Another effect of reflection is the mirage, which occurs 
when the air near the surface is warmer than the layers 
above it, and when the reflection from this warm air layer 
reaches the eye of the observer. It often gives rise to an 
appearance like that of a sheet of water ; and travelers in 
desert lands, where this phenomenon is common, are often 
led to think that they are actually approaching a lake. One 
very commonly sees such an appearance as this at the sea or 
lake shore when distant coasts appear to rise above the sur- 
face of the water. It sometimes happens that light is 
reflected from a warm layer which is above the observer; 
and then the objects appear upside down. This '^loonung," 
as it is called, is particularly common in Arctic regions; and 



28 PHYSICAL GEOGRAPHY. 

the effect produced is so fantastic and wonderful that nearly 
all Arctic explorers describe it. 

The rainbow is a phenomenon which partly depends upou 
the reflection of sunlight ; biit it is chiefly due to 7'efraction, 
the result being a separation of the several components of 
white light into the colors of the spectrum. Each person 
sees a different rainbow even though two observers may 
stand side by side. The cause for the phenomenon is the 
effeut of raindrops wdiich, being denser than the air, bend 
and separate the rays of white light so that we see the 
component colored rays, just as we do when a sunbeam passes 
through a prism. A rainbow is often produced in the spray 
that rises at the base of a waterfall, and at the distance of 
only a few yards one may see it outlined in the spray. 

Another phenomenon resulting from the combined action 
of refraction and reflection is the ring of light or Jialo which 
often surrounds the sun or moon when their light passes 
through thin hazy clouds in the upper atmosphere. These 
clouds are composed of ice particles, which act upon the light 
in a manner analogous to the effect of raindrops in the 
production of the rainbow. Very remarkable halos are 
formed, particularly in Arctic regions, where the air is often 
filled with minute crystals of ice. Sometimes rings of light 
of very brilliant colors are thus produced. The interference 
Avith light resulting from the presence of Avater or ice in 
clouds often produces a ring of light immediately around 
the sun or moon. These are called coronas, and they are 
often beautifully colored, the colors being arranged in con- 
centric rings with the red on the outside. 

One of the most important of the phenomena of light is 
that of absorption. Many bodies, such as pure air and water, 
allow most of the rays of light to pass through them with little 
change, and such bodies are called transparent. Other sub- 



THE ATMOSPHERE. 29 

stances are only partially transparent, and we know them 
under the name of traiiHhiccnt Ixxlies. Still others whieh we 
know as opctquc do not allow any liglit to pass. Thus objects 
have a red color when they reflect a greater number of the 
i\'d than of tlie*other rays; and other colors are produeed in 
the same way by the absorption of different proportions of 
the rays. 

Electricity and Magnetism. — There are certain phenomena 
of magnetism in the earth whieh seem to exercise a de- 
cided influence upon the atmosphere. The earth is a great 
magnet, and the region of greatest magnetic attraction is 
near Hudson's Bay, toward which the needle of the compass 
})oints in our hemisphere. This may be called the iiiagnetic 
pole. The magnetic condition of the earth is constantly 
changing, both in small daily variations and in annual 
changes, as well as in variations covering many years. 
Occasionally there are magnetic storms, when there is a 
disturbance of magnetic instruments, and when the aurora 
sometimes develops in wonderful complexity and weird 
beauty. This is some electrical effect in the thin upper 
atmosphere ; but our knowledge of these phenomena is ob- 
scure. 

Electricity is produced in the atmosphere by various 
causes, and it is nearly always present ; but only rarely does 
it develop suiHcient intensity to become visible to the eye. 
In thunderstorms and tornadoes, when the air is in violent 
commotion, there is often sufficient electricity to cause vivid 
discharges from one cloud to another, or to the earth. This 
li(/htnhi(/ is an interesting phenomenon, but it does not 
ap[)ear to have a marked influence upon the atmosphere. 
It is apparently an incident. The accompanying sound is 
often changed to a rumble by reverberation and echoes 
among the clouds, and betAveen them and the earth. Often 



30 PHYSICAL GEOGRAPHY. 

in violent thunderstorms the . air is filled with a constant 
roar of thunder. The lightning spark or bolt is sometimes 
a single large spark, or it m^y divide and sub-divide, giving 
a branching type of discharge ; and many interesting irregu- 
larities of direction, color, and form are produced. 

The light from the flash moves with great velocity while 
the sound of the thunder travels slowly, at the rate of 
ordinary sound waves. The sound wave is readily worn 
out, and at a distance of a few miles lightning produces 
no perceptible sound. Heat lightnmg is often the result 
of the reflection among the clouds, or on the horizon, of 
lightning in some far-distant thunderstorm, perhaps en- 
tirely hidden behind the curvature of the earth. 

Heat.^ — Aside from the heat which comes to us from the 
sun, we obtain a certain small but more constant supply from 
the other bodies of space and from the earth itself ; but 
these are relatively unimportant. The radiant energy from 
the sun travels at an enormous velocity as a series of waves, 
which are radiated out from the sun in all directions ; and 
only that small portion of them is received by the earth 
which it happens to intercept in its passage about the sun. 

Some substances allow this energy to pass through them 
with readiness, and these are said to be diathermanous ; 
others absorb heat ; and still others reflect the greater part 
of the rays that come to them. The air is comparatively 
diathermanous, as indeed most transparent substances are. 
The smooth glassy surface of water is a good illustration 
of a substance that reflects much of the radiant energy 
coming to it. On the other hand, while the earth reflects 
some, it absorbs a large quantity of heat ; and this is 

1 The sun is emitting a form of energy which under favorable conditions be- 
comes heat, while under other conditions it takes the form of chemical energy. 
These rays are therefore properly radiant energy until ti'ansformed to heat. 



T/IK ATMOSPIIEUE. 31 

particuhirly triu^ for parts of the earth whicli are (hirk 
in coh)r. 

Tlie rays that enter the atniospliere pass tliroiii^h it with 
little interference, because it is diathermanous ; l)nt if there 
is much dust or water va})or in it, a considerable share of the 
rays are intercepted. Thus chnids effectually check the 
passage of many of the rays, and therefore cloudy days arc 
cool. The same tendency exists when the atm()si)here is very 
hazy; and in the late afternoon wlien the solar rays pass 
throug'li a great thickness of air (Fig. 16), the amount of 
heat that reaches the earth is very much less than that 
which comes to the surface at midday. 

Since different parts of the earth's surface l)c]iave dif- 
ferently toward the radiant energy, there is much A'aria- 
tion in the effect produced. This is particularly well 
illustrated by the very marked difference in l)ehavior be- 
tween water and land. Tlie rays that reach the water sur- 
face are in part reflected back into space and thus lost, so 
far as the earth is concerned. Much of that which remains 
raises the temperature of the water ; but as the specific 
heat of the water is high, its temperature is raised very 
slowly. Some is used in the evaporation of the surface 
layers ; and in that case the heat is transformed to tlic 
so-called " latent heat," ^ which does not become a[)})arent 
until the vapor is condensed to water. Moreover, the water 
surface is in motion ; and this tends to distribute the heat, 
and thus to prevent the excessive warming of the ocean 
surface. Therefore for these various reasons, even at the 
equator the ocean surface remains relatively cool. 

On the other hand, land reflects very little of the radiant 
energy, and it is a- solid body, in which neither evaporation 

1 The old term is still used, though perhaps heat of vaporization would 
"be better. 



32 FHYSICAL GEOGEAPHY. 

nor motion is possible. The earth is distinctly not diather- 
manous, and the greater part of the rays which reach it are 
absorbed by the surface portions. Therefore during the 
day the ground tends to Ijecorae warmed by a,bsorption ; 
and this peculiarity is responsible for many of the phenomena 
of the atmosphere. 

Pure air is very slightly wai'med l)y the passage of the 
direct rays of the sun. The small amount of heat thus 
obtained is slightly increased by a supply received from the 
rays which the earth reflects ; but much more is ol)tained 
from the supj^ly which the earth absorbs. All bodies in 
space are radiating a form of energy, either that which 
belongs to them or that which is radiated to them ; there- 
fore the earth is at all times emitting rays by direct radi- 
ation. During the daytime the amount radiated is less 
in quantity than that received from the sun ; but at night, 
when this supply is cut off, the process of radiation proceeds 
so far that the earth loses much of the heat which it had 
received. Radiation is interfered with by the presence 
of clouds or dust ; and hence nights which are cloudy or 
hazy are warmer than those which are clear. 

By the process of conduction^ all bodies which are warmed 
tend to transmit their energy to cooler portions. This is 
well illustrated when a cold iron is placed upon a warm 
stove. In the same way, the air in contact with the warmer 
earth is thus warmed by conduction ; but neither air nor 
earth are good conductors of heat, and if tins process were 
unaided, the effect would be slight and confined to those 
lower layers of the air which were almost immediately in 
contact with the earth. It is a property of gases that when 
heated they are expanded and thus caused to move. By this 
means a process of convectioyi is started which is analogous 
to the boiling of water, and the warm lower layers of air 



THE ATMOSl'HEUE. 33 

I'isc above tlic sui-racc, tln-ir plac(\s luMiio- taken l)y otlun- 
layers w liicli How in toward the point of ascent. 

This process of convection is one of the most important 
in meteoroh),L;'\\; for upon it in larq-e measure (le}ien(ls the 
formation of the winds and otlier features of atnn)spheric 
eircuhition. When air rises it ex])aiids, and in the process 
of expansion cools dynamically, the rate of coolinjjf being 
l.()° for every 300 feet of ascent; and descending air, as 
a result of compression, tends to warm. This feature of 
cooling on ascension gives rise to the formation of many 
of the clouds and rainstorms. 

Thus the air is warmed, partly by the rays which come 
direct from the sun; partly by those which are reflected 
from the earth; partly by those emitted from the earth 
by the process of radiation ; but mainly by conduction 
from the warm eartlfs surface and the convectioual rising of 
these warmed layers. Highlands are cooler than lowlands, 
largely because the air m these ])laces is less dense than that 
nearer the sea level (Fig. 15). The presence or absence 
of hirge bodies of water very markedly modilies the effect 
of solar energy upon the atmosphere. As a result of these 
differences, the atmosphere is put in motion, Avinds are pro- 
duced, clouds are formed, storms are started, and rains are 
caused. 

The movements of the earth in space also give rise to 
many variations in heat effect and atmospheric phenomena. 
As a result of the rotation of the eartii, the greater part 
of its surface is lighted and warmed once every twenty-four 
hours, and cooled once during that time. 

A second important movement of the earth is that of 

revolution, which causes the seasons (Figs. 8 and IT). 

Since the pole is inclined to the plane of revolution, the 

sun is made to- appear to migrate in the hepvens. During 

]> 



34 



PHYSICAL GEOGBAPHY. 



our winter, wlien the sun is verticul over that part of the 
earth which lies between the equator and the tropic of 
Capricorn, the sun rises in the soutliern part of the heavens, 
and passes westward without rising higli toward the zenith. 
Then in Arctic latitudes, the sun does not rise above ■ the 
horizon ; and therefore in this region there is no alterna- 
tion of day and night. In the winter season, in temperate 






Fig. 17. 
Diagram to show the inclination of the sun's rays in different parts of the earth 
during the various seasons. Upper figure, spring and autumn; right-liand 
figure, northern winter; left-hand, northern summer. 

latitudes the journey of the sun across the heavens occupies 
a small fraction of the whole day ; and therefore in such 
regions the time during which the earth is receiving heat 
is less than the length of the night, during which almost 
none is received. 

Besides this fact of short days and long nights, the 
angle at which the rays reach the surface is much 



THE ATMOSPHERE. 



35 



more oblique than in the summer season ; and before reach- 
ing the surface they are obliged to pass through a great 
thickness of atmosphere. These facts make the effect of 
the small amount of energy that does come, less apparent in 
winter than h\ summer, when many of the rays pass from 
a point near the zenith through a relatively small amount 
of atmosphere, reaching the surface more nearly at right 
angles (Fig. 17). After the sun has passed north of the 
equator, summer comes to the northern hemisphere, while 
winter prevails south of the equator. 

Thus at any pomt between equatorial and Arctic regions, 
there are two variations in the effect of the solar rays, one 
a daily and the other a seasonal variation. Tlie tempera- 
ture of the air over the land normally rises during the 
day, and falls at night ; it rises in summer, and falls in 
winter ; and the amount of daily rising and falling is 
greater in winter than in summer. There is much variation 
in these respects according to latitude; and there is less 
change in temperature between day and night, and between 
seasons, at the equator than in other latitudes; but the 
amowit of heat received there is greater than in other parts 
of the earth. The greatest range in temperature, both 
seasonal and daily, is experienced near the Arctic circle. 
The least heat supply is received in polar latitudes; and 
here there is a great range between the summer and 
winter temperatures, but slight daily ranges, because in 
winter the sun does not rise above the horizon, while in 
summer it does not set. 

Moisture. — When rays of radiant energy enter a water 
body, they are in part transformed to " latent heat," being 
engaged in the process of changing the liquid to a gaseous 
condition. By this process of evaporation much of the 
energy exists in a form which is not apparent as heat so 



36 PHYSICAL GEOGBAPHY. 

long as the vapor condition lasts; but when the vapor is con- 
densed, this store of heat becomes apparent. Evaporation 
will take place even from a snow surface ; but the most 
favorable conditions for the production of water vapor are 
warm air in contact with a water surface. 

The capacity of the air for water vapor is limited ; and 
when no more can be contained it is said to be saturated. 
An air in which there is little vapor is constantly capable 
of taking more until the limit of saturation is reached. We 
commonly say that dry air can absorb vapor. ^ If the amount 
of water upon the land is slight, the air in these places 
remains dry ; but naturally this cannot be the case with air 
over bodies of water, for there the conditions favor satu- 
ration. In the interior of c()ntinents, and in the upper 
layers of the atmosphere, there is the smallest proportion 
of water vapor. If the air from these places reaches the 
oceans, it may bring to them conditions of dryness, which, 
however, are soon changed to relative dampness. With the 
air in movement, saturation is less liable to occur than 
would be the case if the air were quiet. Therefore winds 
favor evaporation by bringing fresh supplies of air, and for 
the same reason they tend to prevent saturation. 

The capacity of air for water vapor also depends upon its 
temperature. A layer of air which is saturated at the tem- 
perature of 50*^ becomes relatively dry if its temperature is 
raised to 90°; and an air layer which is nearly saturated at 
90° will be obliged to give up some of its water vapor if the 
temperature is lowered a number of degrees. This is a very 
important point in the formation of clouds, storms, and rains. 
The actual amount of water vapor in the air represents its 

1 Strictly the air does not absorb vapor, but the water vaporizes regardless 
of the presence of the air. However, it is convenient to speak of the capacity 
of the air for water vapor, especially as the air determines the temperature. 



THE ATMOSPHERE. 



37 



absolute humidity ; but tliis is not a very important factor, 
because the same amount of vapor in air of different tem- 
peratures will produce very different effects. 

The point of greatest importance is the relative humidity., 
which is the percentage of water vapor actually contained in 
the air compared with the amount which the air at that tem- 
perature could contain if it were saturated. Thus the relative 
humidity of saturated air at a temperature of 00° is 100 per 





MONDAY 


TUESDAY 


WEDNESDAY 


THURSDAY 




6 XII 6 


6 Xli 6 


6 XII 6 


6 XII 6 












luu 

80 


y 


"\ f 


^ 


_,/" 


AlA- 


^ / 


\ J 


(J 


[^ 




60 
40 
20 




\\r]/[f 











































1 





SEP. II 



12 13 

Fig. 18. 



Diagram showing daily change in relative humidity as a result of the daily 
change in temperature at Ithaca, N.Y. 



cent, for at that temperature no more can be contained ; 
but if the temperature is raised a few degrees, the air 
becomes capable of containing more water vapor, and the 
relative humidity is then less than 100 per cent. The tem- 
perature at which air becomes saturated is known as the 
dew point, for then vapor must be condensed. After a warm 
and apparently dry day, dew may be formed at night merely 
b}' lowering the temperature of the air, and thus increasing 



38 



PHYSICAL GEOGRAPHY. 



1000 FT.1\ Saturated 



the relative humidity, without any change whatsoever in the 
absolute humidity (Fig. 18). 

It follows from this that there must be very marked differ- 
ences in the amount and effect of water vapor contained in 
the air. Over the oceans, the relative humidity is great, and 
the air nearly always near the point of saturation ; in the 
tropics, where the temperature is high, the absolute humidity 
is high, because warm air can contain much vapor ; and on 
mountain peaks, where the temperature is 
low, the amount of vapor is slight, because 
cold air has little capacity for water vapor. 
If the dry upper air descends to the earth, 
its absolute humidity is low ; and even if it 
commenced its descent in a saturated condi- 
tion, its relative humidity decreases because 
the temperature rises (Fig. 19); and if air 
currents move from cooler to warmer lati- 
tudes, their capacity for vapor is constantly 
increasing, because they 
grow constantly warmer and 
have a greater j)Ower of 
absorbing vapor. When 
from warm to 




Capacity for vapor 
43° considerably Mcreased. 



Fig. 19. 

Diagram illustrating increase in tempera- they mOVC 

ture of descending air. Starting in a , . ,1 • t ,• 

saturated condition with a temperature COoler regions their relative 

of 40° at 1000 feet, it reaches the surface humidity increases, bccauSC 

with a higher temperature and its ca- ^ . , ,..,-] i . 

pacity for vapor increased, while its tlieir temperature clescencis ; 

relative humidity has decreased. The ^y^^(]^ when air riscS OVCr land 
reverse takes place with ascent. . .-mi 

elevations, or vertically by 
convection, the relative humidity is also increased, because 
it cools by expansion as it ascends ; and under such condi- 
tions the vapor is often condensed in clouds and rain. 

As a result of these varying conditions we get many varia- 
Ijle phenomena. Where the winds are prevailingly dry, and 



THE ATMOSPHERE. 39 

the relative humidity low, desert conditions result ; and 
where moist winds rise over rapidly ascending lands, condi- 
tions of excessive rainfall are produced. With air prevail- 
ingly dry, evaporation is rapid, while in regions of great rela- 
tive humidity, evaporation is slow and small in amount (I^'ig. 
60). Since water vapor contains a store of "latent heat" 
great stores of heat energy are transported from one latitude 
to another by the movements of vapor-laden air currents. 

Pressure. — The air, though so light and apparently almost 
without substance, actually has weight. At the seashore, 
the average weight of the air column is 15 pounds to the 
square inch ; but as we ascend into the air, whether in a 
balloon or on a mountain, the pressure of the air becomes 
less and less. Aside from this difference in air pressure the 
weight of the column of atmosphere at any single point is 
almost constantly changing. This is due to the fact that the 
air is very elastic and is subjected to a complicated series of 
movements. We shall be better able to understand the 
causes for these changes in pressure, and their effects upon 
the atmosphere, after we have examined in more detail the 
subjects of air temperatures and circulation. 

Effect of Gravity. — Heat is constantly tending to drive 
the air from the earth's surface, and therefore to make the 
lower layers less dense ; but opposed to this is the tendency 
of gravity to draw the atmosphere down to the earth. The 
effect of this is to make the lower layers of the atmosphere 
more dense than those above the earth's surface ; but the 
circulation of the air somewhat modifies this effect. Gravity 
is a very important factor in determining the equilibrium of 
the atmosphere ; for its constant tendency is to restore an 
equilibrium which other causes are tending to destroy. 

Effect of the Earth's Rotation. — As the air moves in the 
form of winds or currents, there is a constant tendency to 



40 



PHYSICAL GEOGRAPHY. 




be deflected to one side, as a result of the effect of the 
earth's rotation. This not only tends to turn the currents 
of air, but its influence is also felt in the ocean currents. 

In the southern hemisphere 
the currents are deflected 
toward the left, and in the 
northern hemisphere toward 
the right ; and we common- 
ly speak of the latter as the 
right-hand deflection (Fig. 
20). 

The reason for this deflec- 
tive tendency is to be found 
in the fact that different 
parts of the earth are mov- 
ing at different velocities. 
By revolving an orange or a 
ball around an axis one can 
see that the motion at the equator is much more rapid than 
that at the poles. Each revolution carries every point along 
a circle, but the diame- i,o„ 

ter of the circle de- 
creases toward the pole 
(Fig. 21). Therefore 
in the course of a revo- 
lution a point near the 
equator travels a much 
greater distance than 
one near the pole. .To 
do this, it must go faster, 
since the same period of 
time is allowed. At the equator the rate is 1521 feet a 
second, while near the poles the rate is greatly reduced. 



Fig. 20. 

Diagram to show how the moving currents 
are deflected from a straight line N-S. 




Fig. 21. 

Diagram illustrating the decrease in diameter 

on different latitudes. 



THE ATMOSPHERE. 41 

A current moving toward the equator, from a region of 
slow motion, is constantly reaching latitudes where the angu- 
lar velocity is greater. If the earth were quiet, it would 
move in a straight line, and if the earth's rotation did not 
produce any effect, it would do the same and reach a 
point on the equator toward which it had originally 
started (N-S, Fig. 20). But the earth is rotating toward 
the east, and the current is of course carried along ; 
but in different parts of its course it is carried at differ- 
ent rates. There are therefore two motions, one to the 
south, the other to the east. As the current in its southerly 
course reaches regions with a greater velocity than those 
just left, it lags behind the earth's rotation just a very little. 
In other words, it tends to take to regions of greater velocity 
the velocity of a region with a slower motion. This lagging 
behind turns it to the west, or the right, and as it moves 
from place to place (Fig. 20) it keeps turning little by little, 
until finally its course is very much altered. Currents 
moving northward from the equator pass into regions of 
less velocity and thus run ahead, or turn to the east in the 
direction of the earth's rotation. The same explanation 
holds for the left-hand deflection south of the equator. ^ 

A current moving very slowly will so nearly accommodate 
itself to the change in velocity that the deflective tendency 
is not very effective. Also in those latitudes, such as the 
equatorial (Fig. 21), where the difference in velocity is not 
great, the deflective tendencj^ is not nearly so great as in 
the higher latitudes, where even in a small distance there 
is a marked difference in angular velocity. 

Even in currents moving along east and west lines the 

1 The teacher will do well to illustrate this important point by the use of 
the globe, or better by allowing a marble to run over the face of a rapidly 
revolving wheel which is inclined toward the class. 



42 PHYSICAL GEOGRAPHY. 

deflective effect is apparent, but tliis cannot be easily ex- 
plained in a few words. 



REFERENCE BOOKS. 

See also references at the close of Chapters III.-VII. 
Davis. — Elementary Meteorology. Gmn & Co., Boston, 1894. 8vo. 

$2.10. (Almost all points thoroughly treated in the light of the best 

modern knowledge.) 
Loomis. — Treatise on Meteorology. Harper Brothers, New York, 1870. 

8vo. $1.50. 
Scott. — Elementary Meteorology. Scribner, New York (Agents). Eifth 

edition, 1890. 12mo. $1.75. 
Tait. — Light. Macmillan & Co., New York (Agents). Second edition, 

1889. 8vo. $2.00. 
Capron. — Aurora. E. & F. N. Spon, New York (446 Brown St.), 1879. 

4to. $17.00. 
Guillemin (translated by Thompson). — Electricity and Magnetism. 

Macmillan and Co., New York, 1891. 8vo. $8.00. (Much on atmos- 
pheric and terrestrial electricity and magnetism.) 
Maxwell. — The Theory of Heat. Longmans, Green, & Co. Tenth edi- 
tion. (Edited by Lord Eayleigh.) 1892. 12mo. $1.50. 
Tyndall. — Heat as a Mode or Motion. Appleton & Co., New York 

Fourth edition, 1883. 12mo. $2.50. 

In most good books on physics, the subjects of heat, light, and electricity 
are well treated from the physical standpoint. 

The American Meteorological Journal (monthly, Ginn & Co., Boston) 
contains a record of the progress in the subject, and many original articles 
of general interest. $3.00 a volume ; eleven volumes published. 



By SIR ARCHIBALD GEIKI^, F.R.S., LL.D., 

Directok-General of the Geological Surveys of the United 
Kingdom. 

THE TEACHING OF GEOGRAPHY. 

SUGGESTIONS REGARDING PRINCIPLES AND METHODS 
FOR THE USE OF TEACHERS. 

Second Edition. Cloth. i6mo. 60 cents. 



" Since Dr. Geikie, following the suggestions of the Germans or such geographers 
as Guyot, has developed this rational doctrine in teaching geography, many writers 
and teachers have adopted the new methods, and, as yet, we know of no wiser or 
more suggestive work for teachers of geography than Dr. Geikie's. 

" Any change in old forms or customs is looked upon askance. Even in the 
methods of teaching, reforms are slow, and should be. Our author says: ' Inveter- 
ate habits of use and wont are apt to blind us to the need of change, and any attempt 
to alter the existing system touches many kinds of vested interests. Even those who 
sympathize with the proposals for reform raise their hands in despair and ask where, 
amid the crowds of subjects now demanded, room is to be opened for any new topic 
or lor any expansion of an old one. Without the consciousness our opinions and 
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tions' had the face of novelty; to-day they are accepted as the most correct and 
natural from the ped.igogical standpoint. There is nothing radical about them. 

" Briefly, Dr. Geikie possesses the widest knowledge of geographical facts, and is 
inspired with the truest pedagogic spirit, and knows that the knowledge of facts 
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Further, to the teacher of any subject, this brief treatise on geography will be most 
suggestive in many directions. 

"The State Department of Education has prescribed this book as one of the 
studies for the teachers of this State in connection with the summer normals. A 
more excellent work could not have been recommended." — The Virginia School 
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ELEMENTARY LESSONS IN PHYSICAL GEOGRAPHY. 

Illustrated. i8mo. $1.10. 

" The language is always simple and clear, and the descriptions of the various 
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Questions on the Same, for Use in Schools. 

i8mo. 40 cents. 



GEOGRAPHY OF THE BRITISH ISLES. 

i8mo. 30 cents. 

" Dr. A Geikie is so well known by his able and lucid treatises on geology that 
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